The present invention claims priority from Japanese Patent Application No. 11-062167 filed Mar. 9, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention is utilized as a data storage device for storing a large amount of data. The present invention relates to a technique for performing a simultaneous write or read for a plurality of channels by using a plurality of heads accessing a plurality of rotary memory media such as disks or cylinders. The present invention relates to an information storage device capable of storing an information with high density and of transferring it at high rate. Particularly, the present invention relates to a technique, in which a plurality of heads access a plurality of coaxially rotating rotary storage media and positions of the heads are controlled by using a two-stage actuator construction, and to a signal format therefor.
2. Description of the Related Art
A rotary information storage device, e.g., a disk storage device, for simultaneously writing or reading a plurality of channels of a single rotary storage media or a plurality of storage media by a plurality of heads accessing the storage media has been known. FIG. 1 shows an example of a conventional hard magnetic disk device. In FIG. 1, magnetic material layers are formed on both surfaces of each of coaxially rotating two magnetic disks 11 and 12 and four heads 13 each provided for each surface of the magnetic disks access the magnetic disks. The heads 13 is totally driven by a single actuator 1 to control positions of the heads. Although the number of the rotary storage media is two in the shown example, it may be four or eight in order to increase the storage capacity.
The present inventors have been developed an actuator, which has a two-stage construction, for positional control of a plurality of heads, which is disclosed in Japanese Patent Application laid-open No. H9-330572. FIG. 2 shows the disclosed actuator having the two-stage construction. In FIG. 2, the actuator includes a first actuator 1 for totally driving a plurality of heads 13 and totally controlling positions thereof within a large area and a plurality of second actuators 2 each for driving an associated head to control a position of the associated head within a small area.
In the rotary information storage device shown in FIG. 2, a joint is provided on an intermediate position of each arm having a forward half supporting a head and a rearward half rotatably connected to the first actuator 1, and the second actuators 2 are provided on the respective joints. That is, all of the arms are rotatable simultaneously by the first actuator 1 within a large area and the forward halves of the arms supporting the respective heads 13 are rotatable about the joints, on which the second actuators 2 are provided, in parallel to surfaces of disks within a limited area independently from each other. That is, each second actuator 2 controls a rotation angle of a forward half of the forward half of the associated arm according to a drive signal. The four heads 13 totally are moved in radial direction of the disks 11 and 12 with a rotation of the first actuator 1 and the positions of the four heads 13 are finely controlled within small areas by the second actuators 2 independently from each other.
In general, the important performance of the rotary information storage device depends upon the recording capacity and the data transfer rate. In order to increase the storage capacity of such device, it is usual to increase the recording density of the storage medium, that is, to reduce a distance between adjacent tracks provided on the storage medium and to reduce a distance between the storage medium and the head. Therefore, in the rotary information storage device shown in FIG. 1, which can not control the positions of the heads individually, the accuracy of the head position control limits the recording density. On the other hand, in order to increase the write or read speed, that is, the data transfer rate, the rotation speed of the storage medium must be increased. When the rotation speed of the storage medium is increased, the head position control speed must be increased correspondingly. Therefore, the actuator must be powerful enough and must work precisely.
In view of this, the rotary information storage device shown in FIG. 2 is preferable in increasing the recording density as well as the data transfer rate, compared with the conventional rotary information storage device shown in FIG. 1. That is, in the rotary information storage device shown in FIG. 2, which has the second actuators 2 provided on the joints of the respective arms, it is possible to finely control the positions of the respective heads 13 individually and, therefore, to perform a tracking precisely individually even when the distance between the adjacent tracks is reduced. Further, since it is possible to reduce a length of the forward half of the arm measured from the second actuator 2 to the position of the head, it is possible to increase the position control speed.
In order to utilize the rotary information (disk) storage device shown in FIG. 2, which is provided with the second actuators 2, the control logic and the signal format used in the device shown in FIG. 1 can not be applied to the device shown in FIG. 2 as they are. Further, the present inventors have found that, by utilizing the rotary information storage device shown in FIG. 2, it is possible to continuously utilize the tracks provided on the storage media by alternately controlling the head positions.
The present invention was made in view of the state of art and has an object to provide a head position control unit applicable to a rotary information storage device including a first actuator for totally controlling positions of a plurality of heads within a large area and a corresponding number of second actuators for individually controlling the positions of the heads within a small areas, respectively.
Another object of the present invention is to provide a circuit construction capable of increasing the recording density and the storage capacity of a rotary information storage device.
Another object of the present invention is to improve the data transfer rate of a rotary information storage device by performing the write or read operation by utilizing a plurality of heads simultaneously.
A further object of the present invention is to provide a circuit construction by which a rotary information storage device can effectively utilize tracks provided on a recording media continuously.
Another object of the present invention is to reduce the cost of a rotary information storage device for a given recording capacity.
The present invention is applied to a rotary information storage device according to the present invention comprising three or more heads, which are coaxially rotated to read or write data from or to tracks provided on at least one recording medium, a first actuator for totally driving all of the heads to control positions of the heads totally within a large area and a plurality of second actuators for driving the heads individually to control positions of the heads within small areas, respectively. In the present invention, all of the heads are not used simultaneously for data read or data write. That is, the present invention is featured by that at least one head, which is not in a read or write state, is moved, in advance, to a track to be accessed next during a time period in which other heads execute data read or data write.
The present invention includes a head positioning circuit for controlling the first actuator and the second actuators. The head positioning circuit comprises:
i) a servo tracking unit for positioning the heads to respective track positions; and
ii) a seek unit for moving at least one head, which is not in data read or data write state, to a track position to be accessed next, in advance, during a time period in which two or more heads are in data read or data write state.
The number of the heads each controlled by two kinds of actuators can be increased when the above mentioned structure is used. As also mentioned, all of the heads do not simultaneously perform the data read or data write. At least one of the heads is released from the data read or data write operation and is controlled such that, in order to use the one head for data read or write with a next timing, it is moved in advance to a desired track position of the rotary storage medium. With this scheme, it is possible to continuously perform the data read or write operation throughout the operation time of the rotary information storage device.
In the present invention, it is preferable that the length of data written in the tracks of the rotary information storage media and the length of data read out from the tracks of the rotary storage media are fixed. That is, the present invention comprises a controller including a write control unit for writing an input data having a fixed length on the tracks of the rotary storage media through the heads and a read control unit for converting data read out from the tracks of the rotary storage media into an output data having a fixed length.
The present invention further comprises a driver for cutting out the fixed length data from a continuous data or synthesizing a continuous data from fixed length data. That is, the driver includes a data divider for dividing the continuous input data to the fixed length input data and a data combiner for synthesizing the fixed length output data to a continuous data.
In the present invention, a write or read time of the fixed length data is preferably an integer multiple of a seek time required to make the head movable by the seek unit. Further, times required by the respective heads to write or read a plurality of the fixed length data related to a continuous data are set as a continuous time series so that the tracks on the rotary storage media can be used as a physically continuous track.
The head positioning circuit may comprise a unit, which, when one of the heads is set in a data read or write state, starts the seek operations of the remaining heads substantially simultaneously with the setting of the one head. Further, it is preferable that the head positioning circuit controls the rotary information storage device such that a fixed length data related to a continuous data is continuously written in another (or adjacent) track.
The rotary information storage medium may take in the form of a magnetic disk, an optical disk, a magneto-optical (MO) disk or other disk. Further, although a single rotary storage medium may be used in the present invention, it is possible to use two, four or more rotary storage media, by employing a structure in which a plurality of rotary storage media are mechanically coaxially supported on a single rotary shaft. It is of course possible to increase the number of the heads for accessing the rotary storage media.
With such construction of the rotary information storage device, it is possible to record data on the rotary storage media without leaving any area of the rotary storage media, which is left unused. Further, it is possible to read or write data continuously in time. Therefore, the effective recording density is increased and the cost for unit amount of information (mega-byte) to be recorded can be reduced. Since it is possible to substantially eliminate the latency for read or write, it is possible to increase the data transfer speed.